IMP, Lanzhou
This paper gives the detectors used for slowly extracted heavy ions from CSR. The beam profiles are measured with viewing screens and anode-striped ion-chambers. The currents are determined with scintillators and ion-chambers. The signal processing system and the measurement results are also presented.
DESY, Hamburg
For current and future accelerators, in particular light sources, high availability is an important topic. Therefore the causes of beam losses must be diagnosed and eliminated as fast as possible. This paper presents a concept using the following signals and data from diagnostic instruments and other sources:
- software alarms transmitted by the control system,
- hardware alarms received and timestamped by the machine protection system, and
- Post-Mortem-Analysis.
MPI-K, Heidelberg
The University of Liverpool, Liverpool
This contribution describes an optical fibre sensor based on the use of a silicon photomultiplier (SiPM) composed of an array of Single Photon Avalanche Detectors (SPADs). This sensor will be used for the detection and localization of particle losses in accelerators by exploiting the Cerenkov Effect in optical fibres. As compared to conventional vacuum photomultipliers, the SPAD array allows for maximizing the geometrical efficiency of Cerenkov photon detection. The array can be directly integrated into the fibre end while retaining the same quantum efficiency (20%) in the wavelength range of interest. The SiPM is intrinsically very fast due to its small depletion region and extremely short Geiger-type discharge, which is in the order of a few hundreds of picoseconds. Therefore, the combined use of optical fibres and SiPMs seems a promising option for a modern Cherenkov detector featuring subnanosecond timing, insensitive to magnetic fields, capable of single photon detection and allowing for the possibility of realization in the form of a smart structure. We present the layout and operating principle of the detector, its characteristics, and outline possible fields of application.
JASRI/SPring-8, Hyogo-ken
RIKEN/SPring-8, Hyogo
Fiber-based beam loss monitors offer the possibility to detect beam losses over long distances, with good position accuracy and sensitivity at a reasonable cost. For the undulator section of the SPring-8 X-FEL, radiation safety considerations set the desirable detection limit at 1 pC (corresponding to a 0.1% beam loss) over more than a hundred meter. While a theoretical approach offers some hints, the selection of the optimum fiber is not straightforward. Glass fibers of different diameter (100 to 600 μm), index profile (graded/stepped) and from three different makers were therefore characterized (signal strength, dispersion, attenuation) at the SPring-8 Compact SASE Source (SCSS), a 1/16th model of the future X-FEL. Beam tests (Fujikura SC400) showed that, at 250 MeV, the detection limit corresponding to a 10 mV signal is below 1 pC over 60 m and 3 pC over 120 m. The position accuracy was found to be better than 30 cm. Finally, the fiber lifetime has been estimated to be over 13000 h from dose measurements at the SCCS.
CERN, Geneva
The LHC Beam Loss Monitoring (BLM) system is one of the most complex instrumentation systems deployed in the LHC. As well as protecting the machine, the system is also used as a means of diagnosing machine faults, and providing feedback of losses to the control room and several systems such as the Collimation, the Beam Dump and the Post-Mortem. The system has to transmit and process signals from over 4'000 monitors, and has approaching 3 million configurable parameters. This paper describes the types of configuration data needed, the means used to store and deploy all the parameters in such a distributed system and how operators are able to alter the operating parameters of the system, particularly with regard to the loss threshold values. The various security mechanisms put in place, both at the hardware and software level, to avoid accidental or malicious modification of these BLM parameters are also shown for each case.
CERN, Geneva
A novel radiation hardened current digitizer ASIC is in planning stage, aimed at the acquisition of the current signal from the ionization chambers employed in the Beam Loss Monitoring system in CERN accelerator chain. The purpose is to match and exceed the performances of the existing discrete component design, currently in operation in the Large Hadron Collider (LHC). The specifications include: a dynamic range of nine decades, defaulting to the 1pA-1mA range but adjustable by the user, ability to withstand a total integrated dose of at least 10 kGray in 20 years of operation and user selectable integrating windows, as low as 500ns. Moreover, the integrated circuit can be employed to digitize currents of both polarity with a minimum number of external components and without needing any configuration. The target technology is IBM 130 nm CMOS process. The specifications, the architecture choices and the reasons on which they're based upon are discussed in the paper.
CERN, Geneva
A discrete components design of a current digitizer based on the current-to-frequency converter (CFC) principle is currently under development at CERN. The design targets at rather high input current compared to similar designs, with a maximum equal to 200mA and a minimum of 1nA, as required by the ionization chamber that will be employed in the Proton Synchrotron and Booster accelerators as well as in the LINAC. It allows the acquisition of currents of both polarities without requiring any configuration and provides fractional counts through an ADC to increase the resolution. Several architectural choices are being considered for the front-end circuit, including charge balance integrators, dual-integrator input stages, integrators with switchable-capacitor, in both synchronous and asynchronous versions. The signal is processed by an FPGA and transmitted over a VME64x bus. Design, simulations and measurements are discussed in this article.
IFIC, Valencia
A set of two Inductive Pick-Up (IPU) prototypes with its associated electronics for Beam Position Monitoring (BPM) in the Test Beam Line (TBL) of the 3rd Compact Linear Collider (CLIC) Test Facility (CTF3) at CERN were designed, constructed, and tested by the IFIC team. One prototype and two units of the series production are already installed in the TBL line. In the first part of the paper we describe the characterization tests of these two prototypes carried out at CERN, and the first beam tests performed to one of them. The second part of this paper is dedicated to the description of the issues addressed by the start of the series production and the characterization tests of the first series units performed with a custom-made low-frequency wire setup. This setup which emulates the beam position variation allows to carry out the series tests in an automatized manner and with higher accuracy.
CERN, Geneva
KEK, Ibaraki
UW-Madison/PD, Madison, Wisconsin
For the LHC beam loss measurement system the high voltage supply of the ionisation chambers and the secondary emission detectors is used to test their connectivity. A harmonic modulation of 0.03 Hz results in a current signal of about 100 pA measured by the beam loss acquisition electronics. The signal is analyzed and the measured amplitude and phase are compared with individual channel limits for the 4000 channels. It is foreseen to execute an automatic procedure for all channels every 12 hours which takes about 20 minutes. The paper will present the design of the system, the circuit simulations, measurements of systematic dependencies of different channels and the reproducibility of the amplitude and phase measurements.
KEK, Tsukuba
RCNP, Osaka
We have continuously developed the Optical Transition Radiation (OTR) monitor with optics system based on the Newtonian telescope to measure a profile for a high intensity proton beamline. Now we installed the OTR monitors of production version on the J-PARC hadron beamline, and successfully observed a first OTR light. This led to the establishment of high S/N profile measurement with minimum beam disturbance. At this commissioning stage, a beam intensity is as small as 1.2 KW, but expected to increase up to 750 kW, so that maintenance work becomes important. To improve ease of maintenance, we plan to replace the focusing lens system with reflective mirror system with higher resistance to radiation. A result of beam profile measurement, an estimation of dependence of an OTR background on a beam loss, and a future plan for an upgrade of our optics system will be presented.
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Berlin
DESY, Hamburg
Local beam losses and beam profiles at particle accelerators are determined by measuring the ionizing radiation outside the vacuum chamber. Four different fiber optic radiation sensor systems will be presented. Two are based on the increase of radiation-induced attenuation of (Ge+P)-doped multimode graded index fibers, whereas with the third system detects the Cerenkov light generated by relativistic electrons in radiation hard fibers. The used fiber is an undoped multimode step-index fiber with 300 um core diameter. Dosimetry at high dose levels uses the radiation induced Bragg wavelength shift of Fiber Bragg Gratings. The selection of a suitable fiber for the individual application is an important requirement and depends on the type, doping, used wavelength and annealing behavior. In addition, the dose range, dose rate and temperature must be considered. At six accelerators all systems are used for in-situ beam optimization and dose measurement. This paper summarizes the basic of this measurement technology and the experience at linear accelerators and at storage rings.
